The judge is too stupid to throw the case out because of false witnesses.
Ostensibly, that's the prosecutor's job, to weed out cases where the evidence is weak.
Now that it's in court, the fact that there is a witness (no matter if the witness is a known liar) will be used as justification to subject Zimmerman to the ordeal. Statute that spares him the ordeal, notwithstanding.
The legal system in Florida is a joke anyway. Great moneymaker for the insiders (judges, prosecutors, lawyers), and, they get to make it up as they go along.